Khanna Ajay, Shedge Sapana V, Zuehlsdorff Tim J, Isborn Christine M
Chemistry and Biochemistry, University of California Merced, Merced, California 95343, USA.
Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA.
J Chem Phys. 2024 Jul 28;161(4). doi: 10.1063/5.0217080.
Accurately modeling absorption and fluorescence spectra for molecules in solution poses a challenge due to the need to incorporate both vibronic and environmental effects, as well as the necessity of accurate excited state electronic structure calculations. Nuclear ensemble approaches capture explicit environmental effects, Franck-Condon methods capture vibronic effects, and recently introduced ensemble-Franck-Condon approaches combine the advantages of both methods. In this study, we present and analyze simulated absorption and fluorescence spectra generated with combined ensemble-Franck-Condon approaches for three chromophore-solvent systems and compare them to standard ensemble and Franck-Condon spectra, as well as to the experiment. Employing configurations obtained from ground and excited state ab initio molecular dynamics, three combined ensemble-Franck-Condon approaches are directly compared to each other to assess the accuracy and relative computational time. We find that the approach employing an average finite-temperature Franck-Condon line shape generates spectra nearly identical to the direct summation of an ensemble of Franck-Condon spectra at one-fourth of the computational cost. We analyze how the spectral simulation method, as well as the level of electronic structure theory, affects spectral line shapes and associated Stokes shifts for 7-nitrobenz-2-oxa-1,3-diazol-4-yl and Nile red in dimethyl sulfoxide and 7-methoxy coumarin-4-acetic acid in methanol. For the first time, our studies show the capability of combined ensemble-Franck-Condon methods for both absorption and fluorescence spectroscopy and provide a powerful tool for simulating linear optical spectra.
由于需要纳入电子振动和环境效应，以及进行精确的激发态电子结构计算，准确模拟溶液中分子的吸收光谱和荧光光谱具有挑战性。核系综方法能够捕捉明确的环境效应，弗兰克 - 康登方法能够捕捉电子振动效应，最近引入的系综 - 弗兰克 - 康登方法则结合了这两种方法的优点。在本研究中，我们展示并分析了使用组合系综 - 弗兰克 - 康登方法生成的三种发色团 - 溶剂体系的模拟吸收光谱和荧光光谱，并将它们与标准系综光谱、弗兰克 - 康登光谱以及实验结果进行比较。利用从基态和激发态从头算分子动力学获得的构型，直接比较了三种组合系综 - 弗兰克 - 康登方法，以评估其准确性和相对计算时间。我们发现，采用平均有限温度弗兰克 - 康登线形的方法生成的光谱与弗兰克 - 康登光谱系综的直接求和几乎相同，而计算成本仅为其四分之一。我们分析了光谱模拟方法以及电子结构理论水平如何影响二甲基亚砜中7 - 硝基苯并 - 2 - 恶唑 - 1,3 - 二氮杂萘 - 4 - 基和尼罗红以及甲醇中7 - 甲氧基香豆素 - 4 - 乙酸酯的光谱线形和相关的斯托克斯位移。我们的研究首次展示了组合系综 - 弗兰克 - 康登方法在吸收光谱和荧光光谱方面的能力，并为模拟线性光谱提供了一个强大的工具。
